This invention relates to an improved lubricating composition, and more particularly this invention relates to a lubricating composition containing an additive combination having improved antioxidation properties.
Hydrocarbon oils are partially oxidized when contacted with oxygen at elevated temperatures for prolonged periods. The internal combustion engine is a model oxidator, since it contacts a hydrocarbon motor oil with air under agitation and at high temperatures. Also, many of the metals (iron, copper, lead, nickel, etc.) used in the manufacture of the engine and in contact with both the oil and air are effective oxidation catalysts which increase the rate of oxidation. The oxidation in motor oils is particularly acute in the modern internal combustion engine, which is designed to operate under heavy workloads and at elevated temperatures.
The oxidation process produces acidic bodies within the motor oil which are corrosive to typical copper-lead and cadmium engine bearings. It has also been discovered that the oxidation products contribute to piston ring sticking, the formation of sludges within the motor oil and an over-all breakdown of viscosity characteristics of the lubricant.
Several effective oxidation inhibitors have been developed by lubricant industries and their employment has been utilized in almost all of the conventional motor oils today. Typical of these inhibitors are the sulfurized oil-soluble organic compounds, such as sulfurized sperm oil, sulfurized fatty acid esters, sulfurized terpenes, sulfurized polybutenes, etc., as well as zinc dithiophosphates and the oil-soluble phenolic and aromatic amine antioxidants. These inhibitors, while exhibiting good antioxidation properties, are burdened by economic and oil-contamination problems. It is preferred to maintain the sulfur content of the oil as low as possible while at the same time receiving the benefits of the antioxidation property. A need, therefore, exists for an improved antioxidant that is stable at elevated temperatures, that can be employed at reduced concentrations and that is economical and easy to produce.
It is an object of this invention to provide additive compositions for lubricants and industrial oils which impart improved antioxidation properties. It is a further object of this invention to provide a synergistic composition having antioxidation properties. It is still another object of this invention to provide lubricating oil compositions having improved antioxidation properties. A further object of this invention is to provide a method of inhibiting oxidation of motor oils.
Other additional objects will become apparent from the following description of the invention and accompanying claims.